function tableBackgroundCorlor(){
  
    let table_tr=document.getElementsByTagName('tr_row')

    for(i = 0; i < table_tr.length; i++){          
       //manipulate rows
           if(i % 2 == 0){
               table_tr[i].className = "even";
           }else{
               table_tr[i].className = "odd";
           }      
         }
     


}